need advice on drivetrain modification

[camlifter]

the spacing between gears on a casset is to narrow for regular bike chain, the chain will rub the sprockets on either side of it. you could get around this by taking the casset apart and removing 1 or 2 of the sprockets and making thicker spacers to go between the sprockets.
sounds like a good idea if you can make a derailer that will work on the left side, thats going to be hard as there designed to work on the right side and the alignment will be way off.
heres a link to the 3sp jack shaft i built. i used a 4 stroke but it could be made to work with a 2 stroke. been some people here who have used multi speed rear hubs with a shifter kit to good effect too.

http://motorbicycling.com/f37/3-speed-jack-shaft-11499.html

 

[bigbutterbean]

actually, i took a look at it today. the stock chain fits on the cassette. the only problem i see is if i have six gears, i can still only have a four speed. the reason being that the gears arent wide enough for the stock chain to occupy two gears that touch each other. in other words, if there are 6 gears, and i use the stock chain, and the engine is driving 6th gear, i cant use 5th gear. i can only use gears one through four. however, if i could use a slightly thinner chain, i might still be able to have a 5 speed transmission. i also calculated gear ratios and rpms today. i figured out that at my current gear ratio and top speed, my engine has a top rpm of about 2000. depending on how i configure the gearing on the new transmission, i could possibly attain a top speed of around 70 mph. if i configure it a different way, my top speed of around 32 which is close to my current top speed. what i dont know is what gear ratios will give me the highest amount of torque. i have calculated all possible gear ratios that would be attainable. the highest gear ratio i could attain would be 9.11:1. the lowest would be 2.12:1. where in that range will i get the best torque?

 

[nextpimp]

Ummm... No. Not good #'s It's funny how your first guess is either SPOT ON or WAY off. Your gonna NEED a smaller rear sprocket IF you can mount it to work. 44t .. **** even 36t on a 26 in tire is just WAYYY tall. 32t would be nice.. some killer low gears and a nice cruising top. Those #s are off dude...trust me.

 

[bigbutterbean]

umm..............NO. youre wrong. first of all no guessing on my part. secondly, any given gear ratio will either produce more speed or more torque, not both. the highest possible ratio i could achieve is 9.11:1. that gear happens to produce the lowest speed, 17 mph. therefore, it will produce the highest torque. i am figuring it will produce twice as much torque as my current gear ratio of 4.40:1. it is definitely half the top speed. i used a gear ratio calculator program and ran every possible number through it. how is a 44t sprocket too tall? its pretty close to the same size of a mountain bikes front chainring sit. if it works there, it will work here. besides, if i take it to a machine shop, they will know how to make it work or they will figure it out. as far as the numbers go, i know they are right.

 

[bigbutterbean]

just to prove it, i will run the numberss with a 40t, 36t, and 32t rear sprocket as soon as i get a chance. right now im going to a cookout so it will haver to wait. besides, for what i want, these gear ratios are fine. there is no right or wrong here, because this is MY idea.

 

[nextpimp]

Its wrong because its not "useable" ratio. let me try to type this out.... I tend to be a bit short and to the point. You said your going from engine (10t) to largest cluster sprocket (Shimano megarange 34t normal ..28t?) Your "top" gear would be your next usable set down on the cluster. No matter how i kick the numbers around w a 44t rear I cant get a final drive LOWER than the original 4.4:1 which means no cruising... You're building a rev box....You'll get a torque increase without acceleration... at the COST of acceleration. There's no ... mechanical benefit in the system.... UNLESS you want a "tractor bike" How else can i say it.... A chihuahua will beat beat you bike in the 1/4 mile, and your bike... if chained to a tree could probably pull itself apart... j/k, but truth is often said in jest.

Don't get me wrong.. its a GREAT idea... The light bulb was a GREAT idea... Getting it to work.... That's where its at my friend.

Just trying to help and keep it cheap.. Under $60 for me personally. This has once again got me looking for a cheaper jackshaft setup... and you know the problem isn't the j-shaft its the mounting. Thats for another thread though. Making it SHIFT is gonna be hard part... If you want to emulate a BIG rear sprocket..t. go ahead and weld that sucker up.

I should also add that i have run the #'s w your 44t.. my 41t .. a 36t and a 32t. Assuming a max rpm 7k on a 26' wheel. 32t just gives a MUCH more useable range IMHO

 

[bigbutterbean]

I dont think you know what the (blank) you are talking about. quit telling me the numbers are wrong. Let me type this out... if i have to answer you again, i will type it out one letter at a time. i used an online gear ratio calculator. here is how the program works. you enter then number of teeth on each gearset and it computes the final ratio. you also type in the wheel size and the engine rpms. it uses all that info to calculate top speed. the mountain bike hub has six gears. the biggest gear has 29 teeth, and the smallest has 14 teeth. if i make it so the engine drives the 29 tooth gear, and use the other gears to shift through, my top speed will range from 17 to 32 mph. that is what the calculator told me. say im wrong again, and i will go to your page and block you.

 

[bigbutterbean]

I dont think you know what the (blank) you are talking about. quit telling me the numbers are wrong. Let me type this out... if i have to answer you again, i will type it out one letter at a time. i used an online gear ratio calculator. here is how the program works. you enter then number of teeth on each gearset and it computes the final ratio. you also type in the wheel size and the engine rpms. it uses all that info to calculate top speed. the mountain bike hub has six gears. the biggest gear has 29 teeth, and the smallest has 14 teeth. if i make it so the engine drives the 29 tooth gear, and use the other gears to shift through, my top speed will range from 17 to 32 mph. that is what the calculator told me. say im wrong again, and i will go to your page and block you.

 

[nextpimp]

ok.. now that ive got some of your numbers... I see where you got 9.11:1 .... show me where you get your 2.12:1 and this idea flies. Right now i cant get you below 4.56:1 ... and thats assuming your next gear down is a 28t(tallest possible gear) ... Since you saying max 32mph ... yours probably a 24t right? That would be a 5.32:1 final ... Your calculator is fine.. i think. And Im not saying its not a useable gearset. Just it doesnt produce any higher gears. No lower rpm gears. Still... may not be a bad step for a hilly area.

 

[bigbutterbean]

ok....here are the numbers.....engine 10t. the hub has 6 gears. 6th gear 29t which will be driven by the engine. 5th gear 26t, 4th gear 23t, 3rd gear 20t, 2nd gear 17t, 1st gear 14t. the rear sprocket is 44t. where i got the 2.12:1 was if I made the engine drive 1st gear instead of 6th gear. dont worry about that, because i am not going with that configuration. i want torque more than speed. if my math is right, my current top speed will only take a small dent with the new transmission and i could also double the torque. if im right, thats worth it.

 

[nextpimp]

No Sir .... You're right. Sorry again if i came off harsh... but i didnt have to do the math on the 2.12:1 ... it just sounded wrong ... the following was a removed edit


***EDIT... Since I'm sensing some hostilities ...

About Me:

The ORIGINAL NEXTPIMP ... TransIDEN crew... Aka, NameJacked by AngelaJ. Im nextpimp EVERYWHERE except nextpimp.com. 35yo 2kids. CompSci Major/ Accounting Minor. Phone-hacking is a lifestyle.

Where I'm from The idea of the forum is to MOVE IDEAS FORWARD ... Right wrong or indifferent its POST your ideas, theories, whatever ... So that they can be PUT TO THE TEST, or some that's been there can save you some pain (thanks baird ... rear derailleur is not lookin to hot =D)

The Idea is YOURS ... Im not tryin to steal it... Im tryin to get there with ya... You do know were gonna put WAY more torque through these things than the SPB kit does... This honestly is my biggest concern... were gonna shred the cassette when we try to shift. I got $20 on it. That's not stopping me though.

So ... can we move ON??? I'm hoping a better success rate than the aforementioned light bulb. Are ya with me? ****

That out the way... how we gonna shift this thing =( ... at speed???

another thing... you'll probably only wind up using 2 gears... or were gonna stay at the top of the rpm band through some quick shifts. 1st gear winds out at about 18mph while 5th does 18mph at about 3000 rpm (44t) ... I feel im missing something here ..Im not sure what.. i just envision the thing wound out.. over the powerband through all or most of the middle gears.

 

[bigbutterbean]

i am not an engineer by any means, so if my ideas seem off, dont mind me. but here is an idea. to shift, use a front derailer. you would have to find some way to make it work backwards. also fashion some kind of spring loaded tensioner so the chain can go tight on any gear. honestly, you could be right about the torque. i dont see it as a problem and neither does my dad. he said torque has nothing to do with how the freewheel works. he knows a lot about mechanics. if you want to test it out, feel free. it would be helpful to me to know beforehand instead of being the first person to try it. also, dont want to spend a lot of money having it done at a machine shop if it is going to break down on me.

 

[bigbutterbean]

i missed what you said before about the powerband....the speeds i calculated were all at 2000 rpm's......gear ratios dont change rpm's.....they change speed or torque. one thing i forgot to mention about shifting, you probably would shred it trying to shift at speed....thats why you let off the throttle, hit the shifter, then SLOWLY accelerate again. that should eliminate torque stress on the gears during shifting.

 

[Pilotgeek]

2000 rpm sounds WAY too low for engine rpms... I'd say a max of around 4k-5k?

I see what you're trying to do, and I used to have ideas like this back when I was in my early teens. However, I don't think that this is an efficient way of making this work. A dérailleur works for bike chains, but that's a lot lower power, and it requires a lot precision to make that kind of system work.

 

[bigbutterbean]

ok first of all pilotgeek, the rpm's are correct. i dont know how many times i have to say it, but i ran all my numbers through a gear ratio calculator more than once. at my current gear ratio and top speed, 2000 rpm's is correct. FYI, gear ratio affects speed and torque a lot more than rpm's do. also, i just have rough ideas. as far as whether or not the derailer would work, who knows? i would either take it to a machine shop or a custom bike shop and let them engineer the thing. i am merely a box of ideas. i dont concern myself with which ideas will work better than others. usually, out of the many ideas i have, a working final product does emerge. another thing is, i wont be shifting at speed. i will be slowing down to shift.

 

[bigbutterbean]

ok first of all pilotgeek, the rpm's are correct. i dont know how many times i have to say it, but i ran all my numbers through a gear ratio calculator more than once. at my current gear ratio and top speed, 2000 rpm's is correct. FYI, gear ratio affects speed and torque a lot more than rpm's do. also, i just have rough ideas. as far as whether or not the derailer would work, who knows? i would either take it to a machine shop or a custom bike shop and let them engineer the thing. i am merely a box of ideas. i dont concern myself with which ideas will work better than others. usually, out of the many ideas i have, a working final product does emerge. another thing is, i wont be shifting at speed. i will be slowing down to shift.

 

[Pilotgeek]

You seem very fixated on this "Gear Ratio Calculator". What if the calculator is wrong? You can run numbers all you want, but it doesn't mean the numbers are meaningful in practice. Crap in, crap out.

Do you know how a 2-stroke works? RPMs do INDEED affect torque. I was saying that you should probably calculate using a higher engine RPM, as it's likely not at it's peak torque at 2000rpm. For example, when you calculated something about going at 70mph
@ 2000rpm. That is not happening.

I'm not going to argue with you about this, I'm just gonna sit and watch you find this out yourself (as you obviously won't listen to anyone else's logic). I think that you have good intentions, but you need to do your research before going out to a machine shop. And by research, I don't mean entering a few numbers into some online calculator.

BTW: Machine shops typically don't "Engineer something for you".

 

[nextpimp]

Be Nice PG ... Thanks for joining the convo. Im just trying to cover the P's .. you know.

Prior Proper Planning Prevents Piss Poor Production. Slowing down to shift ISNT going make much of a difference IMO... Reason, We're Still direct drive Right??? Even IF you slow down that cassette is going to be MOVING FAST. Backing off the throttle will reduce the load BUT we're still talking about slide shifting UP a rear cassette doing AT LEAST 1000 RPMs AT the cassette at any given time. My money is REALLY on a shredded cassette. Unless we can find a way to adapt a rear derailleur.

Sidenote: Me personally I WANT my logic challenged every step of the way. Makes a much stronger final product.

EDIT: I FOUND IT!! =D Didnt take that long either. Its DanielMia's bike. Redundant i know but it shows the issue we all have with 2k rpm. I guess we didn't think it was worth saying... it is WAY too low. 2k is JUST above idle. My #'s have been at 7k ... I did some reverse math a while back and figured i spun my old engine around 9k ALOT. Those tachs are like $30 btw. They got $50 ones that monitors the head temp too... another thread.

http://www.youtube.com/watch?v=64YfAmY7tO8